(Gemini-type Alkyl-polyoxyalkylene-modified Silicone)
A conventional and mainstream surfactant has been that of a linear type composed of one hydrophilic part and one hydrophobic part. However, in recent years, developments have been made in next-generation surfactants such as those of Gemini-type or multi chain-type having multiple hydrophilic and hydrophobic parts. Further, Gemini-type surfactants having a modified structure of hydrophobic, hydrophilic and linking groups have been synthesized, and their performances have been analyzed as well.
A Gemini-type surfactant has a critical micelle concentration lower than that of a linear-type surfactant, and can help achieve a surface activity of the same level as a linear-type surfactant even when used in a very small amount. Therefore, the total amount of a surfactant used in a chemical product can be reduced in such case, and attention has thus been drawn to such Gemini-type surfactant not only as a surfactant capable of improving the productivity of a procedure where a surfactant is used, but also as an alternate environment-conscious material capable of reducing environmental burdens.
In the case of a linear-type surfactant, it is inevitable that given distances exist among the surfactant's molecules due to intermolecular repulsion. In contrast, a Gemini-type surfactant allows its linear part to be oriented close to an interface, thereby making it possible to form a dense and higher-order molecular aggregate(s). In addition, many Gemini-type surfactants are superior in properties such as emulsifying capacity, dispersibility and bubble characteristics.
In the case of a silicone oil, hydrocarbon groups and siloxane chains in a general surfactant are inferior in compatibility, which often constitutes a destabilizing factor when emulsifying the silicone oil. As a countermeasure, there may also be used in combination a silicone-type surfactant having a siloxane part. However, a problem has been that it is difficult for a silicone-type surfactant to form a solid and higher-order molecular aggregate(s) at an interface due to the amorphous nature of siloxane bonds, and that a sufficient stability cannot be ensured accordingly.
Moreover, as a silicone-type surfactant having a siloxane framework in the hydrophobic part, a surfactant having such Gemini-type structure is disclosed in Patent document 1. However, since the hydrophilic part of such surfactant is a cationic functional group, there have been limited kinds of emulsification compositions to which this surfactant can be applied.
(Self-emulsifying Defoaming Agent Composition)
As compared to other defoaming agents, a silicone-type defoaming agent has various superior properties. Thus, silicone-type defoaming agents are widely used in industrial processes associated with foam formation, such as those in the chemical industry, food industry, oil industry, textile industry, papermaking industry, paper and pulp industry or pharmaceutical industry. For example, there have been generally used an oil compound-type defoaming agent obtained by mixing a finely powdered silica with a silicone oil such as dimethylpolysiloxane, methylphenylpolysiloxane and methylvinyl polysiloxane; and an emulsion-type defoaming agent obtained by dispersing in water any of these silicone oil compounds and a surfactant. However, such emulsion-type defoaming agent bears a problem that its defoaming performance will be impaired as a result of having the emulsified particles destroyed when exposed to severe conditions such as a high-temperature condition, a highly alkalic condition and a condition where a larger shear force is applied. As an alternative to such emulsion-type defoaming agent, there have been proposed a self-emulsifying defoaming agent (Patent documents 2 to 6) employing both an organopolysiloxane modified by a polyoxyalkylene group(s) and a silicone oil compound.
However, one of the problems with such silicone-type defoaming agent is that its defoaming performance will be impaired, and separated/precipitated matters will occur, as a result of being in contact with a foam liquid, particularly an alkaline foam liquid for a long period of time.
Further, the defoaming performance thereof will deteriorate with time as compared to its initial value, if the process associated with foam formation is prolonged. In such case, extra amounts of the defoaming agent needs to be added, which may lead to various problems owing to massive addition of a defoaming agent, such as a decrease in yield.
Various proposals have been made to solve the above problems and further improve the defoaming performance. For example, there have been disclosed a method of previously hydrophobizing a silica used in an oil compound with chlorosilane or the like (Patent document 7); and a method of treating a silica with a nitrogen-containing organic silicon compound (Patent document 8). However, these inventions only provide proposals on oil compounds, and hardly discuss any approach to improve the defoaming performance through property improvement using a novel dispersing agent.